On-board ammonia generation and exhaust after treatment system using same

ABSTRACT

Often NOx selective catalysts that use ammonia to reduce NOx within exhaust to a harmless gas require on-board storage of ammonia which can be hazardous and inconvenient. In order to generate ammonia in exhaust, the present disclosure increases a NOx concentration in exhaust from at least one combustion chamber, at least in part, by injecting fuel in a predetermined increased NOx generation sequence that includes a first injection during non-auto ignition conditions and a second injection during auto ignition conditions. At least a portion of the NOx is converted to ammonia by passing at least a portion of the exhaust with the increased NOx concentration over an ammonia-producing catalyst.

U.S. GOVERNMENT RIGHTS

This disclosure was made with government support under the terms ofContract No. DE-FC05-97OR22605 awarded by the Department of Energy. Thegovernment may have certain rights in this invention.

TECHNICAL FIELD

The present disclosure relates generally to exhaust after-treatmentsystems with on-board ammonia generation, and more specifically toincreasing NOx concentrations via combustion for generating ammonia usedwith an exhaust after-treatment systems.

BACKGROUND

In order to meet increasingly stringent federal regulations of NOx andother undesirable emissions, engineers are constantly seeking newstrategies of reducing the production of undesirable emissions. Onemethod of reducing NOx emissions is NOx selective catalytic reduction(SCR) systems. These systems use ammonia (NH₃) to reduce NOx to nitrogen(N₂) and water. Although these systems can reduce NOx emissions, NOxselective catalytic reduction systems often require an ammonia storageon the vehicle. Ammonia tanks can consume valuable space within anengine system and must be replenished periodically. Further, because ofthe high reactivity of ammonia, on-board storage of the ammonia can behazardous.

Some of the drawbacks associated with the use of NOx selective catalystscan be eliminated by the use of on-board ammonia generation systems. Forinstance, the on-board ammonia production system set forth in U.S. Pat.No. 6,047,542, issued to Kinugasa on Apr. 11 2000, injects an increasedamount of fuel into one cylinder group within a plurality of cylindersin order to create a rich exhaust from the one cylinder group. The richexhaust is then passed over an ammonia-producing catalyst that convertsa portion of the NOx in the rich exhaust into ammonia. It has been foundthat the efficiency of conversion of NOx to ammonia by theammonia-producing catalyst may be improved under rich conditions. Theexhaust and the ammonia is then combined with the exhaust from a secondcylinder group and passed through a NOx selective catalyst where theammonia reacts with NOx to produce nitrogen gas and water.

Although the Kinugasa method allows for on-board generation of ammonia,the amount of ammonia that can be created is limited. It has been foundthat amount of ammonia produced is dependent on the amount of NOx in theexhaust being passed over the ammonia-producing catalyst. Becausecurrent combustion strategies can only produce a limited amount of NOx,the amount of ammonia created is also limited. Thus, in order to producea sufficient amount of ammonia, a relatively significant percentage ofthe exhaust must be made rich and passed over the ammonia-producingcatalyst, thereby resulting in a significant fuel penalty.

The present disclosure is directed at overcoming one or more of theproblems set forth above.

SUMMARY OF THE INVENTION

In one aspect of the present disclosure, ammonia is generated inexhaust. A NOx concentration in the exhaust from at least one combustionchamber is increased, at least in part, by injecting fuel in apredetermined increased NOx generation sequence that includes at least afirst injection during non-auto ignition conditions and a secondinjection during auto-ignition conditions within the combustion chamber.At least a portion of the NOx is converted to ammonia by passing theportion of the exhaust with the increased NOx concentration over anammonia-producing catalyst.

In another aspect of the present disclosure, an exhaust after treatmentsystem includes at least one combustion chamber that includes a pistonoperable to reciprocate within the combustion chamber. An ammoniaproducing catalyst is positioned in a first section of an exhaustpassage that is fluidly connected to the combustion chamber. A NOxselective catalyst is positioned in a second section of the exhaustpassage that is fluidly connected to the first section and is downstreamfrom the ammonia producing catalyst. At least one fuel injector isoperable to inject fuel into the combustion chamber and is incommunication with an electronic control module. The electronic controlmodule includes an increased NOx generation algorithm that is operableto signal the fuel injector to inject fuel in a predetermined increasedNOx generation sequence that includes a first fuel injection duringnon-auto ignition conditions and a second fuel injection during autoignition conditions within the combustion chamber.

In yet another aspect of the present disclosure, an article includes acomputer readable data storage medium on which an increased NOxgeneration algorithm is stored. The increased NOx generation algorithmis operable to signal at least one fuel injector to inject fuel in apredetermined increased NOx injection sequence that includes commandinga first injection at a timing during non-auto ignition conditions and asecond injection during auto-ignition conditions in a combustionchamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an exhaust after-treatmentsystem, according to the present disclosure;

FIG. 2 is an enlarged sectioned side diagrammatic view of a tip portionof a fuel injector within the exhaust after-treatment system of FIG. 1;

FIG. 3 is a sectioned side diagrammatic view of an upper portion of thefuel injector of FIG. 2;

FIG. 4 is a bottom view of a first spray pattern from the fuel injectorof FIG. 2; and

FIG. 5 is a flow chart of an increased NOx generation algorithm withinan electronic control module of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a schematic representation of anexhaust after-treatment system 12, according to the present disclosure.The exhaust after-treatment system 12 includes at least one combustionchamber 14 defined by an engine cylinder 13. Although the presentdisclosure contemplates only one combustion chamber 14, the exhaustafter-treatment system 12 preferably includes a plurality of combustionchambers 14 divided into a first portion of combustion chambers 14 a anda second portion of combustion chambers 14 b. In the illustratedembodiment, the engine 10 includes six cylinders 13 defining the sixcombustion chambers 14 with one combustion chamber within the firstportion 14 a and five combustion chambers within the second portion 14b. For purposes of this discussion, the combustion chamber within thefirst portion 14 a will be referred to as the first combustion chamber14 a. Those skilled in the art will appreciate that the number ofcombustion chambers 14 in the first portion 14 a and the second portion14 b can be selected based on a desired power output to be produced byan engine included within the exhaust after-treatment system 12, orother factors known in the art. A piston 15 is positioned within eachcombustion chamber 14 and operable to reciprocate within each chamber14.

The first combustion chamber 14 a is in fluid communication with a firstair intake manifold 10, and the second portion 14 b of combustionchambers 14 are in fluid communication with a second air intake manifold11. Although the present disclosure contemplates only one air intakemanifold, by separating the air-intake manifolds, the air intake foreach portions of the combustion chambers 14 a and 14 b can be controlledseparately. Although the present disclosure is illustrated as includingnaturally-aspirated combustion chambers, those skilled in the art willappreciate that the first portion and/or the second portion of thecombustion chambers could be fluidly connected to a forced-inductionsystem including turbohcargers and/or superchargers. The forcedinduction system could increase power output and/or control the air tofuel-vapor ratios within the combustion chambers. Similarly, the poweroutput of each combustion chamber could be controlled by other means,including but not limited to, an air-intake throttle valve. Preferably,the conditions in the first combustion chambers 14 a is lean relative tothe second combustion chambers 14 b.

The first combustion chamber 14 a is preferably fluidly connected to afirst exhaust manifold 27, and the second portion 14 b of combustionchambers 14 are fluidly connected to a second exhaust manifold 28. Thefirst exhaust manifold 27 is fluidly connected to a first section 18 aof an exhaust passage 18, and the second exhaust manifold 28 is fluidlyconnected to a second section 18 b of the exhaust passage 18.

An ammonia producing catalyst 17 is positioned within the first section18 a of the exhaust passage 18. The ammonia producing catalyst 17 isoperable to convert NOx in at least a portion of the exhaust-gas streamfrom the first combustion chamber 14 a into ammonia. The ammonia may beproduced by a reaction between NOx and other substances in theexhaust-gas stream from the first combustion chamber 14 a. For example,NOx may react with a variety of other combustion byproducts to produceammonia. These other combustion byproducts may include, for example, H₂(hydrogen gas), C₃H₆ (propane), or CO (carbon monoxide).

The ammonia-producing catalyst 17 may be made from a variety ofmaterials. In one embodiment, ammonia-producing catalyst 17 may includeat least one of platinum, palladium, rhodium, iridium, copper, chrome,vanadium, titanium, iron, or cesium. Combinations of these materials maybe used, and the catalyst material may be chosen based on the type offuel used, the air to fuel-vapor ratio desired, or for conformity withenvironmental standards, or based upon other considerations known in theart.

Downstream from the ammonia-producing catalyst 17, the first section 18a of the exhaust passage 18 fluidly connects with the second section 18b of the exhaust passage 18 to form a merged portion 18 c of the secondsection 18 b of the exhaust passage 18. A NOx selective catalyst 19 ispositioned in the merged portion 18 c of the exhaust passage 18 suchthat combined exhaust from the first combustion chamber 14 a, theammonia and the exhaust from the second combustion chambers 14 b passover the NOx selective catalyst 19. The NOx selective catalyst 19facilitates a reaction between ammonia and NOx to at least partiallyremove NOx from the exhaust-gas stream in the merged portion 18 c of thesecond section 18 b. For example, the NOx selective catalyst 19 mayfacilitate a reaction between ammonia and NOx to produce nitrogen gasand water, among other reaction products.

It should be appreciated that a variety of additional catalysts and/orfilters may be included in the exhaust passage 18, including, but notlimited to, particulate filters, NOx traps, and/or three-way catalysts.For instance, in the illustrated embodiment, an oxidation catalyst canbe positioned within the second section 18 b upstream from the NOxselective catalyst 19. Because the NOx selective catalyst 19 mayfunction more effectively with a ratio of NO:NO₂ of about 1:1, theoxidation catalyst may be operable to control a ratio of NO:NO₂ in thesecond section 18 b of the exhaust passage 18.

A plurality of fuel injectors 20 are operable to inject fuel directlyinto the combustion chambers 14, and are separated into a first portion20 a associated with the first combustion chambers 14 a and a secondportion 20 b associated with the second portion of combustion chambers14 b. However, non-direct injection for at the first chambers 14 a iscontemplated. Fuel is delivered from a fuel tank 21 to a common rail 22via at least one fuel pump 24 in any conventional manner. The fuel pump24 is generally in communication with an electronic control module 30that controls the pressure output of the pump 24, and hence the pressurein common rail 22, based on desired engine operation. The fuel issupplied from the common rail 22 to each fuel injector 20 via individualbranch passages 23. Each fuel injector 20 may be fluidly connected tothe fuel tank 21 via a return line 25 depending on its mode of operationand control. Thus, fuel not injected into the combustion chambers 14 canbe re-circulated through the system. In the illustrated embodiment, anadditional fuel injector 33 is positioned to inject fuel within thefirst section 18 a of the exhaust passage 18 upstream from theammonia-producing catalyst 17. With appropriately shaped cams, which maybe different from each other, cam actuated fuel injectors could also oralternatively be utilized.

Each fuel injector 20 and 33 is in communication with an article 29 witha computer readable data storage medium via communication lines 26 and34, respectively. The article 29 may be in communication with, or be apart of, the electronic control module 30. The first portion of fuelinjectors 20 a, herein referred to as the first fuel injector 20 a, isin communication with the electronic control module 30 via a first fuelinjector communication line 26 a. Similarly, each fuel injector 20within the second portion 20 b is in communication with the electroniccontrol module 30 via a second fuel injector communication line 26 b.Thus, the injection strategies of each fuel injector 20 can beseparately controlled by the electronic control module 30. A sensor 31,which is operable to sense NOx and/or ammonia, may be positioneddownstream from the NOx selective catalyst 19 and is in communicationwith the electronic control module 30 via a sensor communication line32. Those skilled in the art will appreciate that sensors, such as NOxsensor 31, are readily commercially-available. Other strategies forsensing or predicting NOx concentrations may be available.

Referring to FIG. 2, there is shown an enlarged sectioned sidediagrammatic view of a tip portion of the fuel injector 20 a of FIG. 1.Although any type of conventional fuel injector with only one set ofnozzle outlets can be used, the fuel injector 20 a may be a mixed-modefuel injector that is operable to inject fuel in at least a first spraypattern (shown in FIG. 4) through a first nozzle outlet set 42 and asecond spray pattern, which may be a conventional well known pattern,through a second nozzle outlet set 43. Although not necessary, fuelinjectors 20 b may also be mixed-mode fuel injectors. The first nozzleoutlet set 42 is referred to as semi-homogeneous or homogenous chargenozzle outlet set and has a relatively small average angle theta withrespect to the centerline 40. These outlets may be relatively small andarranged in a showerhead pattern as shown in FIG. 4. The second nozzleoutlet set 43 is referred to as conventional nozzle outlet set typicalof those in the art and has a relatively large average angle alpha withrespect to centerline 40. These outlets are typically associated withfuel injections in the vicinity of piston top dead center as is known inthe art. Thus, the first spray pattern, referred to as a homogeneouscharge spray pattern, includes a relatively small average angle thetawith respect to a centerline 40 of the combustion chamber 14 a. Thesecond spray pattern, referred to as a conventional spray pattern,includes a relatively large average angle alpha with respect to thecenterline 40 of the combustion chamber 14 a. The opening and closing ofthe second nozzle outlet set 43 and the first nozzle outlet set 42 maybe controlled by an inner needle valve member 44 of a second directcontrol needle valve 47 and an outer needle valve member 46 of a firstdirect control needle valve 45, respectively. The fuel injector 20 a hasthe ability to controllably inject fuel through the first nozzle outletset 42, second nozzle outlet set 43, or both.

Referring to FIG. 3, there is shown a sectioned side diagrammatic viewof an upper portion of the fuel injector 20 a of FIG. 2. A first andsecond needle control valves 48 and 49 control the positioning of thefirst and second direct control needle valves 45 and 47, respectively.Both needle control valves 48 and 49 operate in a similar manner and arepreferably three way valves that are substantially identical instructure. The first and second needle control valves 48 and 49 areoperably coupled to a first and second electrical actuators 50 and 51,respectively. In order to open the first nozzle outlet set 42, the firstelectrical actuator 50 is energized, and the first needle control valve48 moves to a position that relieves pressure acting a closing hydraulicsurface of the outer needle valve member 46. The outer needle valvemember 46 can be lifted off its seat by high pressure fuel within theinjector 20 a, and the fuel can be injected through the first nozzleoutlet set 42. Similarly, in order to open the second nozzle outlet set43, the second electrical actuator 51 is energized, moving the secondneedle control valve 49 to a position that relieves pressure acting on aclosing hydraulic surface of the inner needle valve member 44. The innerneedle valve member 44 can be lifted off its seat by high pressure fuelwithin the injector 20 a and inject the fuel through the second nozzleoutlet set 43. Both the first and second electrical actuators 50 and 51can be activated in various timings, including simultaneously, to injectfuel in different sequences and spray patterns. It should be appreciatedthat any fuel injector with the ability to inject fuel in more than onespray pattern may be considered mixed-mode injector for use within thepresent disclosure regardless of the means for controlling the openingand closing of the different nozzle outlet sets.

Referring to FIG. 4, there is shown an example first spray pattern 52.The first spray pattern 52 is illustrated to include 18 nonintersectingplumes 53 that are directed downward with an average angle theta, asshown in FIG. 2. Average angle theta is preferably substantially smallcompared to the average angle alpha of second spray pattern injectedthrough the conventional nozzle outlet set 43. Generally, the enginepiston 15 is farther away from top dead center during non-auto ignitionconditions than during auto-ignition conditions. Thus, in order to avoidspraying the walls of the cylinder 16 and the piston 15 during non-autoignition conditions, fuel can be injected in the first spray pattern 52with the relatively small average angle with respect to the centerline40 of the combustion chamber 14. If fuel is being injected in aconventional manner in auto-ignition conditions when the piston isnearer top dead center, fuel can be injected in the conventional secondspray pattern with the relatively large average angle with respect tothe centerline 40.

Referring to FIG. 5, there is shown a flow chart of an increased NOxgeneration algorithm 35 within the electronic control module 30 ofFIG. 1. The increased NOx generation algorithm 35 is operable to signalthe first fuel injector 20 a to inject fuel in a predetermined increasedNOx generation sequence. The predetermined increased NOx generationsequence includes at least a first fuel injection 36 a during non-autoignition conditions within the combustion chamber 14 a followed by atleast a second fuel injection 37 a during auto-ignition conditionswithin the chamber 14 a. It should be appreciated that the predeterminedincreased NOx generation sequence could include additional early or lateinjections. Those skilled in the art will also appreciate thatauto-ignition conditions within the combustion chamber 14 a generallyoccur when the engine piston 15 relatively close to top dead center of acompression or expansion stroke, and non-auto ignition conditionsgenerally occur when the engine piston 15 is relatively far from topdead center of the compression or expansion stroke. Thus, the first fuelinjection 36 a will mix with air within the combustion chamber 14 a asthe engine piston 15 advances before igniting. The second injection 37 awill ignite upon injection during combustion of the first injection 36a. Although the increased NOx generation algorithm 35 is only incommunication with only the first fuel injector 20 a, the presentdisclosure contemplates the increased NOx generation algorithm beingoperable to signal any number of the fuel injectors, including all ofthe fuel injectors within the plurality 20.

The increased NOx generation algorithm 35 preferably includes a settingalgorithm 39 operable to set a NOx production amount 38 to correspond toan ammonia production amount. The NOx production amount 38 is the amountof NOx being produced from the first combustion chamber 14 a. Theammonia production amount is the amount of ammonia needed to convert anexpected NOx concentration 54 in the second section 18 b of the exhaustpassage 18 to harmless gasses. The increased NOx generation algorithm 35will set the timing and the amounts of the first and second injections36 a and 37 a to generate the NOx production amount 38. Those skilled inthe art will appreciate that the NOx production amount 38 can beadjusted by adjusting at least one of the timing of the first injection36 a, the amount of the first injection 36 a, the timing of the secondinjection 37 a and the amount of the second injection 37 a. Thoseskilled in the art will appreciate that the NOx production amount 38 tothe ammonia production amount within the first section 18 a of theexhaust passage 18 is about 1:1.

The expected NOx concentration 54 from the second group of combustionchambers 14 b will change based on engine operating conditions. Thepresent disclosure contemplates the determination of the expected NOxconcentration 54 by various conventional open or closed loop means. Inthe illustrated embodiment, the electronic control module 30 includes amap with predetermined expected NOx concentrations based on engineoperating conditions, such as engine speed and load. For eachpredetermined expected NOx concentration, there is a corresponding NOxproduction amount and predetermined timing and amounts of the first andsecond injections into combustion chamber(s) 14 a. In addition, the NOxsensor 31 is positioned within the merged portion 18 c of the exhaustpassage to communicate the NOx concentration 31 a and the ammoniaconcentration 31 b to the electronic control module 30. The settingalgorithm 39 may adjust the NOx production amount 38 such that the NOxand/or ammonia concentration 31 a and 31 b downstream from the NOxselective catalyst 19 is at or below a predetermined NOx and ammoniaconcentration amount. It should also be appreciated that the NOx beingproduced within the second portion of combustion chambers 14 b could beincreased in order to match the ammonia production rather than theammonia production being reduced. Those skilled in the art willappreciate that the different injection strategies between the firstfuel injector 13 a and the second portion of fuel injectors 20 b maycreate different power outputs for the combustion chambers in the firstportion 14 a and in the second portion 14 b. Engine vibrations caused bythe possible varying power outputs can be reduced by matching strokecycles of one or more cylinders 13 in order to cause the cylinders tofunction as one cylinder, or other strategies known in the art.

The increased NOx generation algorithm 35 includes a first spray patternalgorithm 36 operable to signal the first fuel injector 20 a to injectthe first injection 36 a in the first spray pattern 52 illustrated inFIG. 4. Because the first injection 36 a occurs during non-auto ignitionconditions within the combustion chamber 14 a, the relatively smallangle of the injection will allow the fuel to be injected within theopen space of the combustion chamber 14 a rather than the on the wallsof the cylinder 13. The increased NOx generation algorithm 35 alsoincludes a second spray pattern algorithm 37 operable to signal thefirst fuel injector 20 a to inject the second injection 37 a in thesecond spray pattern, being the conventional spray pattern. Because thesecond injection 37 a occurs during auto-ignition conditions, the secondinjection 37 a will ignite upon injection. Thus, the first charge willinherently have ignited before the second injection occurs. Thus, thesecond injection 37 a can be injected at a relatively large angle withrespect to the centerline 40 as compared with the first injection 36 a.

INDUSTRIAL APPLICABILITY

Referring to FIGS. 1-5, a method of generating ammonia in exhaust willbe discussed. Although the present disclosure will be discussed for theexhaust after treatment system 12 for a six-cylinder diesel engine, itshould be appreciated that method of generating ammonia could be usedwithin any exhaust after treatment system for a power source. Thisdisclosure may also be applicable to engines that include spark ignitionin at least some combustion chambers.

In order to generate ammonia in exhaust, a NOx concentration within theexhaust from the first combustion chamber 14 a is increased, at least inpart, by injecting fuel in the predetermined increased NOx generationsequence. Although the predetermined increased NOx generation sequenceis illustrated as including only the first injection 36 a duringnon-auto ignition conditions and the second injection 37 a duringauto-ignition conditions, it should be appreciated that additional earlyor late injections could be added to the sequence. Although the amountof fuel injected can vary, preferably the predetermined increased NOxgeneration sequence will create a slightly lean exhaust. Those skilledin the art will appreciate that lean exhaust is exhaust with lambda lessthan one. Lambda is the air-to-fuel ratio divided by stoichiometricair-to-fuel ratio.

The setting algorithm 39 of the increased NOx generation algorithmdetermines the amount and injection timing of the first and secondinjections 36 a and 37 a necessary to create the desired NOx productionamount 38. The setting algorithm 39 is operable to set the NOxproduction amount 38 from the first combustion chamber 14 a tocorrespond to the ammonia production amount necessary to reduce theexpected NOx concentration 54 created by the second group of combustionchambers 14 b. Those skilled in the art will appreciate that the NOxproduction amount 38 can be set by either a closed or open loop system.In the illustrated embodiment, the expected NOx concentrations atvarious engine operating conditions are predetermined and includedwithin a map in the electronic control module 30. Each predeterminedexpected NOx concentration will have a corresponding NOx productionamount 38 from the first combustion chamber 14 a. The map can includethe predetermined amount and timing of each inject to achieve the NOxproduction amount 38 for the expected NOx concentration at the sensedengine operating conditions. These maps can be fine tuned on-board withappropriate sensing combined with a closed loop control algorithm.

In addition to the predetermined map, the NOx sensor 31 may be used tosense the NOx concentration 31 a and/or ammonia concentration 31 bwithin the exhaust downstream from the NOx selective catalyst 19. If theNOx concentration exceeds a predetermined NOx concentration, the settingalgorithm 39 will determine that the there is insufficient ammonia toreduce all of the NOx within the merged portion 18 c of the exhaustpassage 18. The setting algorithm 39 can adjust the NOx productionamount 38 from the first combustion chamber 14 a to correspond to anincrease ammonia production amount that is needed to reduce the expectedNOx concentration 54. In order to increase the NOx production amount 38,those skilled in the art will appreciate that the timing and the amountsof the first and second injections within the predetermined increasedNOx generation injection strategy can be adjusted. For instance, toincrease the NOx production amount 38, while maintaining the slightlylean environment, the timing of the first injection 36 a can be advancedand/or the amount of the first injection 36 a can be increased.

If the NOx sensor 31 senses an ammonia concentration in the exhaust thatexceeds a predetermined ammonia concentration, the setting algorithm 39will determine that there is more ammonia being produced than necessaryto reduce the expected NOx concentration 54. The setting algorithm 39can reduce the NOx production amount 38 to correspond to a decreasedammonia production amount needed to reduce the expected NOxconcentration 54. Those skilled in the art will appreciate that the NOxproduction amount 38 from the first combustion chamber 14 a can bereduced by adjusting the timing and/or amounts of the first injection 36a and the second injection 37 a of the predetermined increased NOxgeneration injection strategy. For instance, while maintaining theslightly lean environment, to reduce the NOx concentration, the timingof the second injection 37 a can be retarded and/or the amount of thefirst injection 36 a can be reduced. Although the present disclosureillustrates the NOx production amount 38 being based on thepredetermined expected NOx concentration from the map and the sensed NOxand ammonia concentrations 31 a and 31 b, it should be appreciated thatthe NOx production amount could be determined based on solely the map orthe sensed concentrations. Regardless of the procedure for setting theNOx production amount 38, the present disclosure can assure that theammonia produced within the first section 18 a of the exhaust passage 18will reduce the NOx concentration within the second section 18 b suchthat very little, if any, NOx and ammonia are present in the exhaustdownstream from the NOx selective catalyst 19.

During each engine cycle, the first fuel injection 36 a occurs duringnon-auto ignition conditions within the combustion chamber 14 a.Preferably, the timing of the first injection 36 a will be sufficientlyearly within the engine cycle to allow some mixing of the fuel with theair before ignition. Thus, the first injection 36 a is referred to as asemi-homogeneous injection that creates a high NOx generatingenvironment within the combustion chamber 14 a. Although the timing ofthe injection can vary, the first injection 36 a may occur generally at80° before top dead center of the compression stroke in the preferredembodiment with the mixed-mode fuel injector 20 a. Because the firstinjection 36 a is preferably injected in the second spray pattern 52shown in FIG. 4, the fuel will spray at a relatively small average anglewith respect to the centerline 40 of the combustion chamber 14 a,thereby reducing the risk of spraying the walls of the cylinder 13 andthe piston 15. However, with the conventional fuel injector, the fuelwill be injected in the conventional spray pattern with the relativelylarge angle with respect to the centerline 40. In order to avoidspraying the walls of the cylinder 13 and the piston 15, the firstinjection 36 a from the conventional fuel injector will occur generallybetween 46-60° before top dead center of the compression stroke. Thus,with the mixed-mode injection the first injection 36 a can occur earlierthan with a conventional injector without diluting engine lubricatingoil due to wall wetting, allowing more time for the fuel within thefirst injection to mix with the air in the cylinder 16. Regardless ofwhether a conventional or the preferred mixed-mode fuel injection 20 ais used, because the first injection 36 a occurs during non-autoignition conditions, the fuel within the combustion chamber 14 a willhave time to partially mix with the air prior to ignition.

As the engine piston 15 advances during the compression stroke, the fuelfrom the first fuel injection 36 a will combust. Generally, the firstfuel injection 36 a will combust around 20-25° before top dead center ofthe compression stroke. Preferably during combustion of the first fuelinjection 36 a, the second spray pattern algorithm 37 of the increasedNOx generating algorithm 35 will signal the fuel injector 20 a to injectin the second spray pattern, being the conventional spray pattern. Thesecond electrical actuator 51 will be activated, thereby lifting theinner direct needle valve member 44 off of its seat and opening theconventional nozzle outlet set 43. Regardless of whether the fuelinjector is the preferred mixed mode injector 20 a or a conventionalinjector, the fuel will be injected at a relatively small angle withrespect to the centerline 40 of the combustion chamber 14 a. It has beenfound that the combination of the semi-homogeneous first injection 36 afollowed by the conventional second injection 37 a creates a greater NOxconcentration within the exhaust than either of the first or secondinjections alone.

As the engine piston 15 retracts during an expansion stroke and/oradvances during an exhaust stroke, the combustion chamber 14 a willreturn to a non-combustible environment. In the illustrated embodiment,the electronic control module 30 preferably will signal the fuelinjector 20 a to inject an additional amount of fuel in thenon-combustible environment during at least one of the expansion strokeand an exhaust stroke. Those skilled in the art will appreciate that theengine piston 15 will be at a relatively substantial distance from topdead center of the compression stroke when the combustion chamber 14 ais in the non-combustible environment. Thus, the fuel injector 20 a mayinject the fuel in the first spray pattern 52, thus avoiding sprayingthe piston and cylinder walls. On the other hand, if cylinder conditionsare relatively hot, as expected, the additional fuel may be sprayed in aconventional spray pattern and vaporized before any wall wetting couldoccur. Thus, this might facilitate allowing the entire invention bepracticed with a fuel injector having only one set of spray holesarranged in a conventional spray pattern. The advancing piston 15 duringthe exhaust stroke will push the exhaust with the increased NOxconcentration and the additional unburnt fuel amount out of thecombustion chamber 14 a and into the first exhaust manifold 27 via anopen exhaust valve. This unburnt fuel can create the rich exhaustconditions desirable for NOx to ammonia conversion without the need forthe additional fuel injector 33 within the exhaust passage. However, inthe embodiment illustrated in FIG. 1, unburnt fuel is added to theexhaust by injecting the fuel into the first section 18 a of the exhaustpassage 18 downstream from the combustion chamber 14 a. The electroniccontrol module 30 can signal the additional fuel injector 33 to injectthe additional amount of fuel in order to create the rich conditionsdesirable for NOx to ammonia conversion over the ammonia-producingcatalyst 17. It should be appreciated that the rich exhaust conditionscan be created by other methods, such as injecting more fuel within thepredetermined increased NOx generation sequence. Although thepredetermined increased NOx generation sequence can create richconditions within the exhaust from the first combustion chamber 14 a,preferably the predetermined increased NOx generation sequence creates aslightly lean exhaust.

The increased NOx within the exhaust from the first combustion chamber14 a is converted to ammonia, at least in part, by passing the portionof the exhaust with the increased NOx concentration over theammonia-producing catalyst 17. In the rich conditions created by theadditional amount of unburnt fuel, the NOx to ammonia conversion withinthe first section 18 a of the exhaust passage 18 is approximately 1:1.

Other exhaust different from the exhaust with the ammonia is createdfrom the second portion of combustion chambers 14 b and flows throughthe second exhaust manifold 28 to the second section 18 b of the exhaustpassage 18. Because more control over timing and amount strategies areavailable with mixed mode injectors, preferably the second portion offuel injectors 20 b are mixed-mode injectors. The exhaust from thesecond section 18 b is mixed with the ammonia in a merged portion 18 cof the second section 18 b of the exhaust passage 18. The combinedexhaust and ammonia is passed over the NOx selective catalyst 19 withinthe merged portion 18 c. Those skilled in the art will appreciate thatthe NOx selective catalyst 19 uses the ammonia to reduce the NOx toharmless gases, such as nitrogen, that are emitted in the exhaust.

The present disclosure is advantageous because it reduces the fuelpenalty associated with the on-board ammonia generation systems. Becausemore NOx can be produced from the predetermined increased NOx generationstrategy, only one combustion chamber 14 a may be needed to providesufficient NOx for conversion to ammonia operable to reduce the expectedNOx concentration 54 from the second portion of combustion chambers 14b. Because only a small percentage of the exhaust stream is needed tocreate the desired NOx concentration, less fuel is needed to create richconditions required for ammonia production over the ammonia-producingcatalyst 17. The reduced fuel penalty conserves fuel and reduces thecost of the exhaust after-treatment system 12.

Moreover, the addition of the second injection 37 a during auto-ignitionconditions not only creates increased NOx concentrations, but alsoreduces a cylinder pressure spike that can be associated with the earlyfirst fuel injections. By injecting the second injection 37 a duringcombustion of the first injection 36 a, any pressure spike within thecombustion chamber 14 a will be reduced, thereby lessening the wear onthe components within the cylinder 16. Further, the ability to injectfuel from the mix-mode fuel injector 20 a in the first spray pattern 54decreases the risk of fuel-in-oil dilution that can be caused byspraying the cylinder walls with fuel during early injections. Thus, theuse of the mixed-mode injector 20 a and the multi-shot injectionstrategy can increase the life of the engine components.

It should be understood that the above description is intended forillustrative purposes only, and is not intended to limit the scope ofthe present invention in any way. Thus, those skilled in the art willappreciate that other aspects, objects, and advantages of the inventioncan be obtained from a study of the drawings, the disclosure and theappended claims.

1. A method of generating ammonia in exhaust comprising the steps of:increasing a NOx concentration in exhaust from at least one combustionchamber, at least in part, by injecting fuel in a predeterminedincreased NOx generation sequence including at least a first injectionduring non-auto ignition conditions and a second injection duringauto-ignition conditions, and igniting the fuel in the combustionchamber; and converting at least a portion of the NOx to ammonia, atleast in part, by passing at least a portion of the exhaust with theincreased NOx concentration in proximity of an ammonia-producingcatalyst.
 2. The method of claim 1 wherein the step of increasing NOxincludes a step of injecting the first injection in a first spraypattern with a small average angle relative to a centerline of thecombustion chamber and injecting the second injection in a second spraypattern with a large average angle relative to the centerline of thecombustion chamber.
 3. The method of claim 1 including a step of addingunburnt fuel into the exhaust, at least in part, by injecting anadditional amount of fuel into a non-combustible environment of thecombustion chamber during at least one member selected from the groupconsisting of an expansion stroke and exhaust stroke.
 4. The method ofclaim 1 including a step of adding unburnt fuel into the exhaust, atleast in part, by injecting fuel into the exhaust passage downstreamfrom the combustion chamber.
 5. The method of claim 1 including thesteps of: mixing the ammonia with other exhaust; and passing the ammoniaand other exhaust over a NOx selective catalyst.
 6. The method of claim5 including a step of setting an ammonia production amount to reduce anexpected NOx concentration from the other exhaust.
 7. The method ofclaim 6 wherein the step of increasing NOx includes a step of injectingthe first injection in a first spray pattern including a small averageangle relative to a centerline of the combustion chamber and injectingthe second injection in a second spray patter includes a large averageangle relative to the centerline of the combustion chamber; and addingunburnt fuel into the exhaust, at least in part, by injecting fuel intothe exhaust passage upstream from the ammonia-producing catalyst orinjecting an additional amount of fuel into a non-combustibleenvironment of the combustion chamber during at least one memberselected from the group consisting of an expansion stroke and exhauststroke.